The invention concerns a helicopter having the features stated in the preamble of claim 1.
The core part of a helicopter is the main rotor. One or more driving mechanisms actuate the main rotor via a transmission and a main rotor mast which is rotatably supported in the housing of the transmission and fastened on the head of the rotor.
The main rotor with its two and more rotor blades, which are hinged on a rotor head and rotatably supported around its longitudinal axis, takes care of not only the lift but also the propulsion. To produce lift, the rotor blades are collectively, that is, synchronously, engaged around an angle formed with the rotation plane. Propulsion is obtained by a cyclic control, that is, the angle of incidence of a rotor blade passes through a maximum and minimum during a revolution of the rotor mast. The position of the extreme values determines the direction of flight.
The helicopter pilot controls the rotor blades by a swash plate which comprises the main rotor mast. The swash plate consists of a stationary part by which so-called scissors are fastened on the housing of a transmission which is axially movable and tiltable in all directions relative to the rotor mast, and a rotatable part which is rotatably supported opposite the stationary part by radial and axial bearings. The rotatable part moves with the stationary part in the axial direction and likewise, makes the tilting movements. It is fastened on the rotor head by other scissors.
The motion of the swash plate is transmitted, via a lever mechanism, to rotor blade mounts on the rotor head, this is done mostly so that the angle of incidence of a rotor blade enlarges as the swash plate approximates the rotor head.
The helicopter pilot adjusts the swash plate for the flying maneuvers via one other lever mechanism. Often situated parallel to the latter are hydraulic servomotors which, on one hand, facilitate the control and, on the other, make possible a superimposed regulation which counteracts the oscillations of the rotor blade that appear.
The highest useable speed of helicopters is limited by rotor-induced oscillations and by the efficiency of the forward flying main rotor. Oscillations and inefficiencies result from non-optimal angles of incidence of the rotor blades relative to the momentary direction and speed of the oncoming flow and from their dynamic characteristic. To counteract said effects, it is advantageous to flexibly control the angle of incidence of the blade. Whirling resulting from abrupt flow on the rotor blades can be controlled, for example, by failure suppressant regulators with the aid of band filters for the first natural torsion frequency of the rotor blades. Thereby noise and vibrations are reduced and the efficiency, the same as the economy, are improved. In addition, the work load of the pilot is diminished.
Two active control systems are basically known (Paper--No. II, 6.3.1., Sixteenth European Rotokraft Forum, Sep. 18-21, 1990, Glasgow "Development and First Tests of Actuators for an Individual Blade Control" Peter Richter, Hans-Dieter Eisbrecher, Valentin Kloppel), namely, the high harmonic control which is superimposed to the control of the swash plate and the actuators of which are situated below the swash plate in the helicopter stationary system, and the individual blade control in which with each rotor blade is associated an actuator in the rotary system between the rotatable part of the swash plate and the rotor blade mounts.
In the high harmonic control, due to the actuators in the helicopter stationary system, high frequency blade angle changes are transmitted, via the swash plate, to the rotor blades. For reasons of geometry only, certain frequencies can thus be transmitted, namely, the so-called blade number harmonic and the immediately adjacent frequencies in a four-blade rotor, therefore, the fourth, third and fifth, the eighth, seventh and ninth, etc. harmonics of the rotor rotary frequency but not the second, sixth or tenth harmonics. The corresponding applies to rotors having more than four blades.
In the individual blade control, there are no limitations relative to the frequencies and signal form, but the constructional effort for the actuators in the rotary system are considerably high due to the additional centrifugal force strains and the energy and signal transmission from the helicopter stationary system to the rotary system. Besides, the fact that each actuator can be individually controlled entails the danger that the rotor blades, in case of failure of operation of the regulation system may move randomly which impairs safety.
The problem on which the invention is based is to provide in a helicopter of the above mentioned type an individual control of the rotor blades that is light weight, of minimal contructional effort, and has good efficiency.